The present invention relates to a technique of estimating the temperature of a driving clutch such as a torque distribution clutch in a four-wheel-drive vehicle or a differential limiting clutch between right and left driving wheels.
A four-wheel-drive vehicle employs, for example, an electronic control clutch for controlling torque distribution between driving wheels and driven wheels. If the torque transmitted through the clutch is large and continues for a long time, the clutch will overheat. To cope with the overheating problem, there is a technique of switching normal clutch control to protective clutch control to disengage the clutch and lower the clutch temperature. A small, light-weight four-wheel drive system installed in, for example, a sport utility vehicle (SUV) must frequently use a clutch to transmit maximum torque when driving a low-frictional road such as a sandy or snowy road. In this case, the protective clutch control must be employed to control the temperature of the clutch.
The protective clutch control needs a clutch temperature as data. The clutch temperature is provided by, for example, a temperature sensor attached to the clutch, or is estimated from torque.
The protective clutch control that obtains a clutch temperature from a temperature sensor must install the temperature sensor on a clutch such as an electronic control clutch. The temperature sensor must withstand severe heat and vibration under which the clutch operates. In addition, the temperature sensor must be protected from breaks or short circuits. These necessities increase the cost of the protective clutch control.
The protective clutch control that estimates a clutch temperature from torque also has problems mentioned below. The protective clutch control is activated when torque of predetermined magnitude continues for a predetermined period. In FIG. 1A, a torque curve I continuously exceeds a threshold value for a period from t0 to t2 that is longer than a criterial period. The torque curve I is small in magnitude, and therefore, generates no heat that exceeds a clutch protection temperature, as shown in FIG. 1B. Accordingly, the torque curve I needs no protective clutch control. However, the protective clutch control starts at t2 when the torque curve I exceeding the threshold value passes the criterial period. This is excessive protection, and therefore the clutch transmits insufficient torque.
A torque curve II of FIG. 1A also exceeds the threshold value for the period from t0 to t2, and therefore, the protective clutch control also starts at t2. The torque curve II is large in magnitude, and therefore, generates beat that exceeds the clutch protection temperature at t1 before t2, as shown in FIG. 1B. This is insufficient protection, i.e., the clutch protection is too late to start.
FIG. 2 shows protective clutch control based on a prior art that resets an estimated clutch temperature whenever an instructed torque value to a clutch falls below a threshold value, although the temperature of the clutch decreases slowly. When the instructed torque alternately rises above and falls below the threshold value, an estimated clutch temperature greatly deviates from an actual clutch temperature because of the slowness of clutch temperature decrease. This deteriorates the reliability of estimated clutch temperatures.
An object of the present invention is to solve these problems by providing an apparatus for estimating clutch temperatures that closely follow actual clutch temperatures. The apparatus employs no temperature sensor, and therefore, is low-cost.
In order to accomplish the object, a first aspect of the present invention provides an apparatus for estimating the temperature of a driving clutch whose engagement including slide engagement is controllable. The apparatus has a clutch speed difference detector that detects a rotational speed difference between input and output shafts of the driving clutch, a torque estimator that estimates torque transmitted through the driving clutch, an energy calculator that calculates energy applied to the driving clutch according to the detected rotational speed difference and estimated torque, a temperature estimator that estimates a clutch temperature variation based on the calculated energy and estimates a clutch temperature based on the estimated clutch temperature variation, and a determination unit that determines whether or not the calculated energy is above a reference energy level. If the calculated energy is determined to be equal to or above the reference energy level, the temperature estimator increases the estimated clutch temperature by an increment, and if the calculated energy is determined to be below the reference energy level, the temperature estimator decreases the estimated clutch temperature by a decrement.
A second aspect of the present invention provides a method of estimating the temperature of a driving clutch whose engagement including slide engagement is controllable. The method includes an operation of detecting a rotational speed difference between input and output shafts of the driving clutch, an operation of estimating torque transmitted through the driving clutch, an operation of calculating energy applied to the driving clutch according to the detected rotational speed difference and estimated torque, an operation of estimating a clutch temperature variation based on the calculated energy and estimating a clutch temperature based on the estimated clutch temperature variation, and an operation of determining whether or not the calculated energy is above a reference energy level. If the calculated energy is determined to be equal to or above the reference energy level, the clutch temperature estimating operation increases the estimated clutch temperature by an increment, and if the calculated energy is determined to be below the reference energy level, the clutch temperature estimating operation decreases the estimated clutch temperature by a decrement.